Material deposition is widely used in window glass coating, flat panel display manufacturing, coating on flexible films (such as webs), hard disk coating, industrial surface coating, semiconductor wafer processing, photovoltaic panels, and other applications. Materials are sputtered or vaporized from a target source and deposited on a substrate. Conventional deposition systems have various drawbacks in material utilization. For example, referring to FIGS. 1A-1E, a deposition system 100 includes a rectangular target 110 above a substrate 115 in a vacuum chamber 120. A stationary magnetron 130 is held above the target 110. The substrate 115 can be transported in a direction 150 relative to the target 110 and the magnetron 130 to allow uniform deposition on the top surface of the substrate 115. A power supply 140 can produce an electric bias between the target 110 and walls of the vacuum chamber 120.
The magnetron 130 (FIG. 1C) includes a magnetic pole 132 of a first polarity and a magnetic pole 135 of a second polarity opposite to the first polarity. The magnetron 130 can produce magnetic flux outside of the sputtering surface 112 on the lower side of the target 110 (as shown in FIG. 1B) to confine plasma gas near the sputtering surface 112. More electrons can be confined near locations where the magnetic field parallel to the sputtering surface 112 and where the magnetic field is the strongest. A closed loop can be formed to trap the electrons by locations having local-maximum magnetic field strength. The closed path can guide the migration path for the trapped electrons near the sputtering surface 112. The closed-loop magnetic field can enhance the ionization efficiency of the sputtering gas (i.e. the plasma) to more effectively confine electrons near the sputtering surface 112. The enhanced ionization can allow lower operating pressure during sputter deposition, which is easier to implement in operation.
A drawback of the deposition system 100 is that it has low target material utilization. After a period of sputtering operations, as shown in FIGS. 1D and 1E, a non-uniform erosion pattern 115 usually appears on the sputtering surface 112 after a period of sputtering operations. The erosion pattern 115 typically includes a close-looped groove that matches the magnetic field strength of the magnetron 130. The most erosion occurs at target locations 116 that correspond to locations having high magnetic field strength where the sputtering gas is enhanced the most. The target 110 has to be replaced before the target locations 116 reach the top surface of the target 110. The target 110 is discarded and the unused target material 117 is wasted.
There is therefore a need to increase the utilization of target materials and to minimize waste in material depositions.